The present invention relates to a backflow valve.
A backflow valve, also known as a backwater valve, is used to prevent a reversal of flow in a flow line. An example of a backflow valve is disclosed in Canadian Patent 2,114,602 and corresponding U.S. Pat. No. 5,406,972 granted to Coscarella et al.
The Coscarella et al reference discloses a backflow valve that has a pivoting closure gate with an open position to accommodate flow in a desired flow direction and a closed position to close off the flow line when there is a reversal of flow. The closure gate is hinged to the bottom of the valve housing. In the open position, flow passes over the closure gate with the closure gate serving as a spillway. Secured to the closure gate is a float. When the level of liquid rises, the float causes the closure gate to rise and the reversed direction of flow pushes the closure gate into the closed position.
The Coscarella et al valve has proven to be an effective backflow valve. The fact that the closure gate in the open position serves as a spillway is not suitable for use with liquids that are highly caustic, leave a residue, or carry debris that can adversely affect the operation of the valve over time.
What is required is an alternative configuration of backflow valve in which the closure gate does not serve as a spillway.
According to the present invention there is provided a backflow valve which includes a valve body with a flow passage extending through the valve body having a longitudinal axis. A closure gate is provided having a first end and a second end. The closure gate is pivotally mounted in the flow passage of the valve body for movement between an open position in which the closure gate is positioned on a plane substantially parallel to the longitudinal axis of the flow passage and a closed position in which the closure gate is positioned transverse to the longitudinal axis. The closure gate has a midsection positioned pivot axis positioned between the first end and the second end. The closure gate is unbalanced with greater weight being toward the first end. A rotational stop is secured to the valve body to limit pivotal movement when the closure gate is in the open position. The greater weight at the first end of the closure gate biases the closure gate by force of gravity against the rotational stop and into the open position. A float secured to the first end of the closure gate causes the closure gate to pivotally move in response to a rise in liquid in the flow passage, with a reversal of flow pushing the closure gate to the closed position.
The flow lines that backflow valves are used with typically are rated at 50% of their flow capacity. This means that the flow line for liquid passing through the flow passage is generally below the longitudinal axis of the flow passage. With the backflow valve, as described above, in the open position the closure gate sits parallel to and above the flow line. The closure gate is only exposed to the liquid when the level of liquid rises due to a reversal in flow.